I'm still of the opinion that motive is more than just grumpy property owner even if SA is a facet. As others have sad, why would RL take that kind of risk with what he had to lose--probation, reverse mortgage, no one to manage his property if he's not there, etc. If it's him, or if he's involved in some sort of multiple person local folks conspiracy, I'm convinced that there is deep history that would elevate the actions to what they were--cold blooded murder.
Who knows what this history could be, but in small towns, the Hatfields/McCoys thing can get pretty crazy, especially if fueled by covert illegal activity or financial shenanigans that damage relationships between clans/families. I am still on the fence as to whether it's RL, but I don't see him going to these lengths for a small provocation.
If it's not RL or someone operating with his knowledge, then I lean towards SA/sport killing by someone, still believe it's a local person.